Smoke-producing composition

ABSTRACT

The composition of this invention contains red phosphorus, magnesium,  sod nitrate, and an epoxy binder. It can optionally contain silica to aid in processing. The magnesium is used to sustain the smoke produced by the red phosphorus for a period greater than 5 minutes for screening of military operations. Further, the composition does not exhibit any increased sensitivity to impact or friction over traditional smoke-producing compositions. This is the case even though the composition contains a high-level of red phosphorus.

GOVERNMENTAL INTEREST

This invention described herein may be manufactured, used and licensedby or for the Government for Governmental purposes without payment to meof any royalties thereon.

This invention relates to an improved smoke-producing composition foruse in sustained military screening without increased sensitivity toexternal stimuli such as friction or impact.

BACKGROUND OF THE INVENTION

Red phosphorus is used as a smoke-producing agent in a number ofammunition items. The red phosphorus burns in the presence of oxygen toform anhydrous phosphoric acid which, when combined with moisture in theair, forms a thick white cloud of smoke. A certain amount of heat inputis required to start the reaction, and this is provided by a match orignition mixture. After the reaction is initiated, exothermic heat aidsin sustaining the smoke-producing process.

If loose red phosphorus powder is ignited, it will react vigorouslybecause adequate air is available to each particle in the powdered mass.However, when the red phosphorus is pressed into a pellet, the air voidsare eliminated. In the latter situation, the oxygen is only available tothe outer surface of the pellet. As a result, reaction can only occur atthe surface of the pellet. Although the reaction is controllable by thelatter pelletized arrangement, sufficient heat is not produced tosustain significant smoke-production. In such a situation, the smoke isoften thin, and of little use in the screening of a military operation.

To produce an adequate smoke-screen, the art intimately mixes an oxygensource into the red phosphorus powder prior to pressing the same into apellet. This solution of the cited problem was found adequate for theintended purpose of the art. The oxygen sources are called oxidizers,and include such ingredients as nitrates, chlorates, oxides andchromates. The nitrates such as sodium nitrate are preferred for usewith red phosphorus to produce a military screen. Sodium nitrate is agood source of oxygen, inexpensive, substantially free of contaminants,and does not render the red phosphorus overly reactive. When thecomposition is overly reactive, it could be explosive.

However, there is a serious drawback with the use of oxidizers in theformulation. As you increase the concentration of oxidizer in a specificformulation, the following are increased, viz: the reaction rate, theheat output, and the sensitivity to various stimuli such as friction andimpact. A concentration of oxidizer in the formulation could be reachedwhere there would be sufficient oxygen available to react with all thered phosphorus in the formulation without the need for additional air.However, at that point, there would be excessive heat output, and thesensitivity would be increased to a dangerous level.

In the art, the concentration of oxidizer in the formulation is belowthe above described concentration so that a controllable reaction willoccur with only sufficient heat to propogate the reaction. To be morespecific, the formulation utilized in the art for the M819 contains 79.5percent red phosphorus and 14 percent sodium nitrate. These pelletsproduce a very large volume of smoke in a 2.5 minute time frame. Whileperformance of this formulation is considered quite good, it falls shortof the desired 5 minute screening requirement. As described, thisformulation produces a very large volume of smoke. In fact, more smokeis produced by this formulation than is necessary for adequate screeningpurposes. If this volume of smoke could be redistributed over a 5 minutetime frame, the requirement for a sustained screen for militaryoperations would be adequately met.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a smoke-producingcomposition which will produce a sustained cloud of smoke in excess of 5minutes for screening of military operations, such composition withoutenhanced sensitivity to external stimuli such as friction and impact.

This invention consists of a composition containing red phosphorus,sodium nitrate, magnesium, and a binder. This composition produces acontrolled output of smoke providing adequate screening of a militaryoperation in excess of 5 minutes. In the composition, the red phosphorusis converted to smoke. The nitrate concentration controls the amount ofoxygen available to the red phosphorus thereby controlling the rate ofreaction and the smoke output. Further, the magnesium providessupplementary heat required by the composition to assure a sustainedreaction rate.

By reducing the sodium nitrate, i.e. the oxidizer, the production ofsmoke is reduced because of a slower burn rate. Also, when the reactionis slowed, the heat output of the reaction is reduced to a level whichis inadequate for sustaining the smoke-producing process at the desiredrate. However, magnesium is a fuel similar to red phosphorus because itburns in the presence of air. Magnesium gives off a great deal of heat,and when added to the composition in granulated form, gives offintermittent surges of heat. Also, fortunately, magnesium does notincrease sensitivity to the cited stimuli.

In the broad sense, the composition of this invention contains thefollowing ingredients in the proportions given, viz:

    ______________________________________                                        Ingredients     Parts by Weight                                               ______________________________________                                        1.      Red phosphorus                                                                            72 to 80                                                  2.      Sodium nitrate                                                                            7 to 10                                                   3.      Magnesium   7 to 10                                                   4.      Binder      6.0                                                       ______________________________________                                    

The composition may also contain 1.25 parts by weight of silica for easeof processing.

Note should be taken, however, that the combined percentage of nitrateand magnesium should be at about 17.0 parts by weight in order tosustain an adequate reaction rate without increased sensitivity toexternal stimuli such as friction and impact.

Further, the oxidizing agent, sodium nitrate, should be present in thecomposition between 7 and 10 parts by weight. If an amount greater thanabout 10 parts by weight is used, the composition becomes increasinglysensitive to impact and friction. Also, the composition will burn toofast to sustain 5 minutes of smoke screening. If the sodium nitrate ispresent in less than 7 parts by weight, the composition is slow toignite and the production rate of smoke is not sufficient to achieve anadequate screen.

Also, the magnesium should be present in the composition between 7 and10 parts by weight. If an amount less than 7 parts is used, the burnreaction does not have sufficient heat to sustain good smoke production.If the amount of magnesium is above 10 parts, the improvement to therate of smoke production is negligible, and the additional magnesiumwould therefore be wasteful.

The epoxy binder of the composition is preferably present at about 6parts by weight. It can be present in an amount between 6 and 8 parts byweight. Below 6 parts, the physical strength and integrity of the pelletcould not be maintained during firing of the munition. Eight parts epoxyprovides more than adequate strength for all current and planned usesfor this composition.

Based on a total of 100 parts of composition (excluding silica) and theallowable variations in other ingredients, the resulting limits in theamount of red phosphorus (72 to 80 parts by weight) will provide for anacceptable amount of red phosphorus to provide good smoke.

PREFERRED EMBODIMENT

To be more specific, the composition JXS-10, contains the followingingredients in the optimum proportions indicated, viz.

    ______________________________________                                        Ingredient              Parts by Weight                                       ______________________________________                                        Red Phosphorus, Technical, MIL-P-211C,                                                                77.0                                                  12 Feb 80, Class 2, extra fine                                                Sodium Nitrate, MIL-S-322B, 5 Feb 68,                                                                 9.0                                                   Grade B, Class 2                                                              Magnesium, MIL-M-382C, 10 Aug 78, Type 1,                                                             8.0                                                   Grade A, granulation 6                                                        EPON 828 Resin, Shell Chemical                                                                        3.0                                                   Versamid V140 Hardener, General mills                                                                 3.0                                                   Silica, MIL-S-14760, 10 May 1968                                                                      1.25   (optional)                                     ______________________________________                                    

The composition JXS-10 was prepared in the following manner, viz.

(a) Pre-mix the resin and hardener, then dilute with acetone to reducethe viscosity of the mix.

(b) Blend the RP, sodium nitrate, epoxy solution, and magnesium withacetone to render the mix to a dough-like consistency. Continue mixinguntil acetone content is 1% by weight.

(c) The silica is added at this point as a flow enhancer.

(d) Granulate the mix through an eight-mesh screen.

(d) Press the material into a pellet under a load of 12000-18000 psi.

(f) Cure the pellet at 140° F. for 48 hours.

In the development of the composition of the present invention, theobject was to take the smoke previously produced for 3 minutes by theconventional composition of the military art, and to distribute suchsmoke produced over a longer period of time. However, when the amount ofnitrate in the conventional compositions was reduced, the rate of smokeproduction was decelerated and the conventional composition haddifficulty in sustaining itself. But, sensitivity to external stimuliwas reduced. To distribute the smoke produced by the conventionalcompositions over a longer period, magnesium was added to thecomposition. The magnesium, when evenly distributed in the compositionprovided a supplementary heat source. Fortunately, such addition ofmagnesium did not contribute to the sensitivity of the compositioncontaining the reduced amount of sodium nitrate. The magnesium was foundto provide intermittent surges of heat for 6 to 7 minutes. These heatsurges supplemented the normal heat of reaction of the composition, andhelped to sustain good smoke production without accelerating thereaction between the red phosphorus and the sodium nitrate.

In previous smoke-producing compositions of the military art, it wasfound that when the amount of sodium nitrate contained therein was about14 percent, a very large quantity of smoke was produced at a highlyaccelerated rate. However, in such a situation, the adequate productionof smoke from such compositions was complete in about 3 minutes. It wasalso found that ignitability and sensitivity of such compositions toexternal stimuli such as friction and impact was extremely high thustending towards a dangerous situation.

The smoke-producing composition of this invention is called the U.S.Army Composition JXS-10. This composition provides an excellent screenof smoke for military operations in excess of 5 minutes which is quiteadequate for its intended purpose. Further, the pellet embodying thiscomposition is less sensitive to external stimuli such as friction andimpact when compared to the conventional smoke-producing compositions ofthis military art.

In conclusion, it has been found that a composition consistingessentially of red phosphorus, sodium nitrate, magnesium and an epoxybinder within critical proportions satisfy the needs of the art foreffective field applications relative military screening operations.

What is claimed is:
 1. An improved smoke composition for use inscreening military operations for a sustained period coupled withreduced sensitivity leading to deflagration from friction or impactconsisting essentially of:(a) red phosphorus being present in an amountbetween about 72 to 80 parts by weight, (b) sodium nitrate being presentin an amount between about 7 and about 10 parts by weight, (c) magnesiumbeing present in an amount between about 7 and about 10 parts by weight,and a (d) a binder being present in an amount of about 6 parts byweight, the additive percentage of said nitrate and magnesium beingabout 17 parts by weight.
 2. The composition of claim 1 including about1.25 parts by weight of silica.
 3. A smoke composition for use inscreening military operations for a period of greater than about 5minutes coupled with reduced sensitivity to friction or impactconsisting essentially of:(a) Red phosphorus present in an amount ofabout 77 parts by weight, (b) Sodium nitrate present in an amount of 9parts by weight, (c) Magnesium present in an amount of about 8 parts byweight, and (d) a binder present in an amount of about 6 parts byweight.
 4. The composition of claim 3 including about 1.25 parts byweight of silica.
 5. An improved smoke producing pellet for use inscreening military operations coupled with reduced deflagrationsensitivity from impact and friction consisting essentially of(a) Redphosphorus present in an amount between about 72 to 80 parts by weight,(b) Sodium nitrate present in an amount between about 7 and about 10parts by weight, (c) Magnesium present in an amount between about 7 andabout 10 parts by weight, and (d) A binder present in an amount of about6 parts by weight, the additive percentage of said nitrate and magnesiumbeing about 17 parts by weight.
 6. The composition of claim 5 includingabout 1.25 parts by weight of silica.
 7. An improved smoke producingpellet for use in screening military operations coupled with reducedexplosive sensitivity to impact and friction, consistimg essentiallyof(a) Red phosphorus present in an amount of about 77 parts by weight,(b) Sodium nitrate present in an amount of 9 parts by weight, (c)Magnesium present in an amount of about 8 parts by weight, and (d) Abinder present in an amount of about 6 parts by weight.
 8. Thecomposition of claim 7 including about 1.25 parts by weight of silica.